1. Field of the Invention
This invention relates to a compound for sealing liquid crystal.
2. Description of the Prior Art
A liquid crystal display unit in which liquid crystal is confined between transparent substrates having driving electrodes for activating the liquid crystal has been so far assembled in the manner as described below.
First, a sealing agent is applied to one of two substrates each having the liquid crystal driving electrode by a screen printing method or by using a dispenser, and the electrode substrates are placed one upon another while putting bead- or rod-like spacer elements therebetween. Then, the sealing agent between the substrates with electrodes is hardened under pressure to seal the liquid crystal between the substrates.
Conventionally, one-liquid thermosetting epoxy resin has been generally used as the sealing agent. Or, it has been proposed to use photo(UV)-setting adhesive consisting of epoxy acrylate for the sealing agent as a principal component (Japanese Patent Application Public Disclosure No. HEI 1-243029(A)).
Although the thermosetting adhesive conventionally used as the sealing agent has excellent moisture resistance, it consumes two or more hours to completely harden by heating, resulting in decrease of workability in assembling the liquid crystal display unit and so on. Disadvantageously, there is a possibility that the electrode substrates between which the liquid crystal is confined do not precisely meet each other and cannot be held leaving a uniform gap therebetween.
On the other hand, the photo(UV)-setting resin which is hardened at room temperature for a short time does not easily cause lateral aberration or dislocation of the electrode substrates and is advantageous in assembling the liquid crystal display unit. However, the conventional adhesive consisting of epoxy acrylate adhesive is insufficient in adhesive strength for securing the substrates for confining the liquid crystal.
An adhesive agent consisting of polyether-modified polyurethane acrylate or polyester-modified polyurethane acrylate as a principal constituent possibly degrades light distribution efficiency required for conducting an experiment to evaluate the properties such as of moisture resistance of the adhesive.
Thus, a sealing agent possessing both properties of photo(UV)-setting functional group and thermosetting functional group has also been proposed, but it is very inferior in preservative stability to a one-fluid epoxy resin. Moreover, since this sealing agent should be exposed to ultraviolet rays, and heated to confine the liquid crystal between the electrode substrates when manufacturing the liquid crystal display unit. Thus, the sealing agent of functional group cannot also improve productivity of manufacturing the liquid crystal display unit.
It has been known that an imidazole compound is used as a latent thermosetting agent for epoxy resin. Also, a compound prepared by treating the imidazole compound with an isocyanate compound, which is used as the latent thermosetting agent for epoxy resin, has been known (Japanese Patent Application Public Disclosure No. SHO 59-27914(A)). The known compound has been commercialized by Asahi Chemical Industry Co., Ltd. of a Japanese company under the name of "Novacure".
U.S. Pat. No. 4,703,338 (Sagami et al.) discloses a resin composition for sealing an electronic device such as a liquid crystal display unit, which comprises a polymerizable vinyl monomer such as acrylated epoxy resin, glycerol mono(meth)acrylate and isobornyl(meth)acrylate.